The invention of the integrated circuit based on silicon and silicon dioxide has allowed in the last decades an enormous development in microchip processor technology and microelectronics. In an integrated circuit, inter alia, n-channel and p-channel transistors are combined for data processing in the so called CMOS logic (complementary metal oxide semiconductor). Transistors basically are resistances controlled by an external gate voltage. In the last decades, the performance of the integrated circuits could be improved by increasing miniaturization of the transistors and thus by the growing transistor density. In the meantime, however, the dimensions of the individual structures of the transistor components are so small that fundamental physical limits are reached and further miniaturization will not lead to an improvement of the circuits.
Meanwhile, besides silicon and silicon dioxide, new materials are used at this place for producing integrated circuits, the physical properties of said materials leading to an improvement of the functionality. Inter alia, the use of III/V semiconductor materials in the CMOS technology is discussed.
Since the electron mobility of some III/V semiconductor materials is substantially higher than that of silicon and the efficiency or switching speed of n-channel transistors is significantly determined, inter alia, by the electron mobility, the use of III/V semiconductor materials as n-channel layers could lead to a substantial improvement of the integrated circuits. Furthermore, the gate voltage can be reduced by using III/V semiconductor materials, which in turn reduces the energy consumption and thus the heat dissipation in the integrated circuits. At present, various institutes, universities and enterprises investigate the use of III/V channel layers in the silicon technology.
Which III/V semiconductor is most useful for the integration on silicon, is determined, on the one hand, by the fundamental properties of the semiconductor material, such as the electron mobility and the electronic band gap.
On the other end, the compatibility for mass production in the silicon technology must ultimately be considered. Arsenic is a substantial constituent of many III/V semiconductor mixed crystals. Due to the high toxicity of arsenic, an envisaged use of arsenic-containing materials in a large-scale industrial production requires an expensive disposal of the arsenic-containing waste products.
For the integration of III/V semiconductor materials on silicon-based circuits, normally the epitaxy method is employed. In this epitaxial precipitation method, the lattice constants of the crystalline semiconductor materials play a decisive role. The used silicon substrate or the carrier substrate in the silicon chip technology determines the basic lattice constant. Most III/V semiconductor materials with high electron mobility have, however, a different lattice constant from that of silicon, which is normally higher. In the epitaxial integration of III/V channel layers on silicon substrate, this difference of the lattice constants leads to the formation of misfit dislocations in the III/V-semiconductor layer. These dislocations are crystal defects, which significantly deteriorate the electronic properties of the semiconductor layer. In order to assure an optimum material quality of the III/V channel layers, special III/V buffer layers are necessary. These buffer layers are defined by a special sequence of different III/V semiconductor materials and/or by a special production method. Furthermore, this buffer layer must not be too thick, so that the compatibility in the III/V-integration on silicon with the actual CMOS process is assured.
Different buffer layers or matching layers are for instance known in the art from the document DE 103 55 357 A.